• BZOJ 4443: 小凸玩矩阵【二分图】


    我是传送门

    先看题目,从数列中选第K小,很容易想到二分或者单调队列,但这里单调队列显得不是那么合适。而任意两个数不在一行一列,这符合二分图的定义,所以思路就很明了了,找出所有的值然后去二分找答案。

    #include <cstdio>
    #include <cstring>
    #include <iostream>
    #include <algorithm>
    #define oo 0x7f7f7f7f
    #define get(x) scanf( "%d", &x )
    #define put(x) printf( "%d", x )
    #define cln(x) memset( x, 0, sizeof(x) )
    using namespace std;
    
    const int R = 255;
    int f[R];
    int p[R];
    int sq[R][R];
    int head[R];
    int to[R<<1];
    int next[R<<1];
    int n, m, k, ans, tot;
    
    void add( int x, int y )
    {
        tot++;
        to[tot] = y;
        next[tot] = head[x];
        head[x] = tot;
    }
    
    int DFS( int x, int t )
    {
        for ( int i = head[x]; i != -1; i = next[i] )
        {
            if ( p[to[i]] != t )
            {
                int y = to[i];
                p[y] = t;
                if ( f[y] == 0 || DFS( f[y], t ) ) 
                { 
                    f[y] = x; 
                    return 1; 
                }
            }    
        }
        return 0;
    }
    
    int solve( int l, int r )
    {
        if ( l > r ) return  l;
        int mid = ( l + r ) >> 1;
        ans = 0;
        tot = 0;
        
        for ( int i = 1; i <= n; i++ ) 
            head[i] = -1;
        for ( int i = 1; i <= m; i++ ) 
            p[i] = f[i] = 0;
        for ( int i = 1; i <= n; i++ )
            for ( int j = 1; j <= m; j++ )
                if ( sq[i][j] <= mid ) 
                    add( i, j );
        for ( int i = 1; i <= n; i++ ) 
            ans += DFS( i, i );
        
        if ( ans >= n - k + 1 ) 
            return solve(l, mid - 1);
        else 
            return solve( mid + 1, r );
    }
    
    int main()
    {
        get(n), get(m), get(k);
        for ( int i = 1; i <= n; i++ )
            for ( int j = 1; j <= m; j++ )
            {
                get(sq[i][j]);
                ans = max( ans, sq[i][j] );
            }
        put( solve( 1, ans ) );
        return 0;
    }

    ↑除了MLE所有错误类型都被我弄出来了,真是伤不起Orz

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  • 原文地址:https://www.cnblogs.com/GuanHuaEdison/p/6920543.html
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